Endovascular prostheses are sometimes used to treat aortic aneurysms. Such treatment includes implanting a stent or stent-graft within the diseased vessel to bypass the anomaly. An aneurysm is a sac formed by the dilation of the wall of the artery. Aneurysms may be congenital, but are usually caused by disease or, occasionally, by trauma. Aortic aneurysms which commonly form between the renal arteries and the iliac arteries are referred to as abdominal aortic aneurysms (“AAAs”). Other aneurysms occur in the aorta, such as thoracic aortic aneurysms (“TAAs”) and aortic uni-iliac (“AUI”) aneurysms.
“Endoleak” is the persistent flow of blood into the aneurismal sac after implantation of an endovascular prosthesis. The management of some types of endoleak remains controversial, although most can be successfully occluded with surgery, further stent implantation, or embolization. Four types of endoleaks have been defined, based upon their proposed etiology, as described below.
A type I endoleak, which occurs in up to 10 percent of endovascular aortic aneurysm repairs, is due to an incompetent seal at either the proximal or distal attachment sites of the vascular prosthesis, resulting in blood flow at the end of the prosthesis into the aneurismal sac. Etiologies include undersizing of the diameter of the endograft at the attachment site and ineffective attachment to a vessel wall that is heavily calcified or surrounded by thick thrombus. Type I failures have also been found to be caused by a continual expansion of the aneurysm neck (the portion of the aorta extending cephalad or caudad from the aneurysm, and is not dilated). This expansion rate has been estimated to be about one millimeter per year. Because the aneurysm neck expands beyond the natural resting diameter of the prosthesis, one or more passageways are defined about the prosthesis in communication with the aneurismal sac. Additionally, Type I endoleaks may be caused when circular prostheses are implanted in non-circular aortic lumens, which may be caused by irregular vessel formation and/or calcified topography of the lumen of the aorta.
Type I endoleaks may occur immediately after placement of the prosthesis, or may be delayed. A delayed type I endoleak may be seen during follow-up studies if the prosthesis is deployed into a diseased segment of aorta that dilates over time, leading to a breach in the seal at the attachment site.
Type I endoleaks must be repaired as soon as they are discovered, because the aneurismal sac remains exposed to systemic pressure, predisposing to aneurysmal rupture, and spontaneous closure of the leak is rare. If discovered at the time of initial placement, repair may consist of reversal of anticoagulation and reinflation of the deployment balloon for an extended period of time. These leaks may also be repaired with small extension grafts that are placed over the affected end. These methods are usually sufficient to exclude the aneurysm. Conversion to an open surgical repair may be needed in the rare situation in which the leak is refractory to percutaneous treatment.
Type II endoleaks are the most prevalent type, occurring in 10 to 25 percent of endovascular aortic aneurysm repairs, and are characterized by flow into and out of the aneurismal sac from patent branch vessels. These endoleaks are most often identified on the post procedural CT, in which these leaks appear as collections of contrast outside of the endograft, but within the aneurismal sac. The most frequent sources of type II endoleaks are collateral backflow through patent lumbar arteries and a patent inferior mesenteric artery. Because the sac fills through a collateral network, the endoleak may not be visualized on the arterial phase of CT scanning; delayed imaging is thus required.
Type III and type IV endoleaks are much less common. Type III endoleaks represent flow into the aneurismal sac from separation between components of a modular system, or tears in the endograft fabric. Type IV endoleaks are due to egress of blood through the pores in the fabric. Type IV leaks heal spontaneously, while type III leaks are repaired with an additional endograft to eliminate systemic flow and pressure in the aneurysm.
As can be readily appreciated, even with the successful implantation of an endovascular prosthesis, failures may occur thereafter. It has been found that type I failures may affect up to 5-10% of all implanted prostheses. Accordingly, there is a clear need for an endovascular prosthesis which can reduce the likelihood of, and ideally eliminate, type I failures.
U.S. Pat. No. 7,044,962 to Elliott describes an implantable prosthesis with a radially-expandable tubular body and at least one skirt extending therefrom. The skirt in his invention terminates in a peripheral edge. At least portions of the peripheral edge are free and displaceable to a greater diameter of the tubular body. Thus, with the implantable prosthesis being a stent-graft used to treat an aortic aneurysm (e.g., AAA), the skirt may be used to inhibit type I endoleaks upon its selective displacement in response to irregular aortic shaping and/or aneurysm neck expansion. The skirt may actively inhibit type I endoleaks by forming a physical barrier against flow between the tubular body and the aortic wall. In addition, the skirt may passively inhibit endoleak formation by sufficiently restricting blood flow to allow coagulation and clot formation, which would act as a barrier against endoleakage.
U.S. Pat. No. 4,938,740 to Melbin describes a technique in which diseased portions of a blood vessel, such as with an aneurysm, are ablated and replaced with a prosthetic member. This technique, however, requires open surgery. As an improvement over this technique, endovascular emplacement techniques have been developed to implant grafts and stent-grafts into a vessel from a remote puncture site, thereby obviating the need for open surgery. For example, an endovascular prosthesis (stent or stent-graft) is positioned to bypass the aneurysm with the ends of the prosthesis being in contiguous contact with healthy portions of the aorta, the prosthesis having been introduced endovascularly (e.g., with a catheter). Accordingly, if the aneurysm were to rupture, blood flow through the aorta would be uninterrupted, and internal bleeding generally avoided.
PCT Publication WO 2008/107885 to Shalev et al., and US Patent Application Publication 2010/0063575 to Shalev et al. in the US national stage thereof, which are incorporated herein by reference, describe a multiple-component expandable endoluminal system for treating a lesion at a bifurcation, including a self expandable tubular root member having a side-looking engagement aperture, and a self expandable tubular trunk member comprising a substantially blood impervious polymeric liner secured therealong. Both have a radially-compressed state adapted for percutaneous intraluminal delivery and a radially-expanded state adapted for endoluminal support.
The following references may be of interest:    U.S. Pat. No. 5,824,040 to Cox et al.    US Patent Application Publication 2006/0229709 to Morris et al.    US Patent Application Publication 2006/0241740 to Vardi et al.    US Patent Application Publication 2008/0109066 to Quinn